八千万美国人不需要补充维生素D

Nearly 80 million Americans would no longer need to take vitamin D supplements under new Institute of Medicine guidelines, according to a study by Loyola University Chicago Stritch School of Medicine researchers. Results were published Oct. 24, 2012 in the journal PLOS ONE.

The new guidelines advise that almost all people get sufficient vitamin D when their blood levels are at or above 20 nanograms per milliliter (ng/ml). Older guidelines said people needed vitamin D levels above 30 ng/ml.

Holly Kramer, MD, MPH and colleagues examined data from 15,099 non-institutionalized adults who participated in the Third National Health and Nutrition Examination Study (NHANES III). The sample included 1,097 adults who had chronic kidney disease, which has been linked to low vitamin D levels.

In the survey population, 70.5 percent of adults with healthy kidneys had vitamin D blood levels that would be considered insufficient under the older guidelines. But under the newer Institute of Medicine guidelines, only 30.3 percent of these adults had insufficient vitamin D levels.

Among adults with chronic kidney disease, 76.5 percent had insufficient vitamin D under the older guidelines, while only 35.4 percent had insufficient levels under the Institute of Medicine guidelines.

Because NHANES III is a representative sample, researchers were able to extrapolate（推断） results to the general population. Kramer and colleagues estimate that a total of 78.7 million adults considered to have insufficient vitamin D levels under the older guidelines would now have sufficient levels under the Institute of Medicine guidelines. "The new guidelines have an impact on a large proportion of the population," Kramer said.

The Institute of Medicine guidelines are based on nearly 1,000 published studies and testimony from scientists and other experts. (The Institute of Medicine committee that wrote the new guidelines for vitamin D and calcium includes Ramon Durazo-Arvizu, PhD, a professor in Loyola's Department of Preventive Medicine and Epidemiology).

The Institute of Medicine committee found that vitamin D is essential to avoid poor bone health, such as rickets. But there have been conflicting and mixed results in studies on whether vitamin D can also protect against cancer, heart disease, autoimmune diseases and diabetes, the Institute of Medicine committee found. Moreover, excessive vitamin D can damage the kidneys and heart, the committee reported.

However, the Institute of Medicine guidelines are controversial. For example, the Endocrine Society continues to endorse the older guidelines. Kramer said that people who are confused about how much vitamin D they need should consult with their doctors.

Kramer is first author of the study, which was funded by the National Institutes of Health. She is an associate professor in Loyola's Department of Preventive Medicine and Epidemiology and Department of Medicine, Division of Nephrology and Hypertension. Her co-authors are Durazo-Arvizu; Guichan Cao, MS; Amy Luke, PhD; David Shoham, PhD; and Richard Cooper, PhD of Loyola's Department of Preventive Medicine and Epidemiology and Chris Sempos, PhD of the National Institutes of Health's Office of Dietary Supplements.